Ammonium nitrate explosives and their manufacture



l 13,004,842 AMh/IONIUM NITRATEEXPLOSIVES AND THEIR MANUFACTURE Hugh Charles Rowlinson, Beloeil, Quebec, Canada, assignor to Canadian Industries Limited, Montreal, Quelice, Canada, a corporation of Canada No. Drawing. Filed Dec. 1, 1958, Ser. No. 777,220 Claims priority, application Canada Feb. 4, E58

. 6 Claims. (Ci. 52-14) emit: Patented, Oct. 17,-

Depending upon the sensitivity desired, sufiicient foaming agent to provide a volume of from to 50% gas by volume of the composition may be added. A composition e apable ef being=initiated ey =a blasting cap weuld' erally require from 25% to 50% gas by volume of the 10 composition. For initiation by a boosting charge, such as The present invention relates tocastammeaiamrdtrate 4 00 grams dynamite only iromahoutld? to-25.% r

explosives and to a process for producing such explosives. I Ammonium nitrate is a commercially desirable explosive since it can be provided relatively cheaply. To be an by volume of the composition is generally required. In the case of hydrogen peroxide, which is a preferred foaming agent, aqueous solutions of from 1% to 50% E 0 effective explosive, however, the ammonium nitrate charge give good results. The density of the cast explosive commost'be employed in crystalline or granular form and used under conditions of large diameter charge or of tight confinement. Such substances as carbon black and fuels have, in the past, been admixed with the ammonium nitrate to position can in most cases be calculated from the volume of gas which thefoaming agent is capable of releasing.

The foaming agent is best dispersed into the molten mixture of ammonium nitrate and fuel immediately before the achieve higher efliciency and sensitivity to initiation of melt is cast, but may be added at any stage of the mixingdetonation.

Explosive compositionscontaining, in addition to crystalline or granular ammonium nitrate, fuels which are not explosives when used by themselves are generally of inoperation.

The fuel used according to the present invention is com-v bustible matter which is not explosive under ordinary conditions when used by itself and which in burning readily sufiicient density to sink readily in water. When loading reacts with oxygen with the evolution of considerable such explosives under water it is important that they should sink, that is, a density of over 1.0 g./cc. would be required. Moreover, increased density increases the detonation speed and shattering effect of the explosive.

volumes of gaseous compounds. The fuel should preferably be non-volatile at the temperature at which it is added to the ammonium nitrate'melt to reduce to a mini mum losses by way of evaporation. Also, the fiashpoint It is an object of the present invention, therefore, to of the fuel must obviously be above the temperature of the provide an ammonium nitrate explosive composition of increased density.

A further object of the invention is the provision of such m ammonium nitrate explosive composition possessing high sensitivity to initiation of detonation.

In an endeavour to cast explosive charges (a way of increasing density), such as are used for filling cartridges, shells or like containers, it has been proposed, if necessary with the aid of an emulsifying agent, to emulsify fused ammonium nitrate and explosive organic compounds. Such cast charges have, however, been found to be insufliciently sensitive to be initiated by an ordinary commercial detonator.

It has now surprisingly been found that highly sensitive cast ammonium nitrate explosive compositions including a fuel can be obtained by including in the composition before casting a substance thatu ill prrrvideeagasshus modtmt is;

ammonium nitrate melt;

Among the fuels which may be used according to the present invention may be mentioned higher boiling mineral hydrocarbon fractions such as diesel oils, parafiin waxes and tars, glyceride animal or vegetable oils or fats, and many other organic and inorganic compounds such as urea, ethylene glycol, terpenes, rosins, cellulosic materials, graphite, aluminum and ferrosilicon, and mixtures thereof.

In general it is desirable to add from 2% to 20% by weight of fuel, from 4% to 8% by weight being preferred for hydrocarbon fuels. To sensitise the composition of the invention even further, a part of the fuel may be replaced bya high explosive compound selected from the group consisting of trinitrotoluene, pentaerythritol tetranitrate and cyclo-trimethylene trinitramine.

To achieve intimate mixing of the ammonium nitrate Jiliih the fuel it may b necessary to employ an gmulsify-j ing agent. When the fuel acts as its own emulsifying agent, such as is the case with certain long chain organic amines, little or no additional emulsifying agent may be required. Generally, however, it is advisable to add from 0.10% to 2.0% of. a standard emulsifying agent, for example fatty acid soaps or other anionic or non-" ionic surface active agents, to attain readily the homogeneous consistency required. Generally the amount of emulsifying agent required will not exceed 0.75% of the dry weight of the emulsion. As emulsifying agents there may also be employed colloidal substances soluble or of the gas so composition.

Thepresent invention provides, therefore, a process for casting an ammonium nitrate explosive composition which comprises mixing to a substantially homogeneous consistency an ammonium nitrate melt, a fuel and a foaming agent and allowing the mixture so obtainedto solidify into desired shapes.

The present invention also provides a cast ammonium nitrate explosive having a substantially solid structure with gaseous pockets dispersed throughout the structure, Which structure is obtained by intimately mixing, and subsequently cooling, an ammonium nitrate melt, a fuel and a foaming agent.

of the ammonium nitrate melt, for instance, agar-agar,

dextrin, gum tragacanth and cellulose glycollate.

It is usually convenient to-carry out the emulsifica'tion at a temperature between C. and C. although higher temperatures maybe employed with proper safes" guards. f

Pure ammonium nitrate melts at C. but impurities present in the commercially'obtainable compounds depress this'temperaturesomewhat. Various compounds adapted to lower the melting point ofthe ammonium; nitrate'and capable of forming lower-meltingeutectic mixtures with it may be used. Suchcompounds maybe anhydrous and of'oxidisingcharacter and these include,'-;

for example, metal nitrates. However, urea, and even water, may be used for the purpose of depressing the melting point of ammonium nitrate.

If desired, other ingredients of various types employed in the manufacture of explosive compositions may be introduced into compositions of the present invention. After casting the composition into moulds they may be water-proofed by applying, for example, a coating of a wax or pitch, by a dip or spray treatment. It may also be convenient, at times, to prepare compositions according to the present invention in quarrying sites and the like by casting them directly into boreholes.

The invention will now be further illustrated by way of the following examples, in which the parts are parts by weight.

Example I 79.4 parts of dry ammonium nitrate were melted at about 140 C. with 17.9 parts of urea. The mixture was cooled with stirring to 105 C., at which temperature it was a slurry of crystals and liquor. 1.46 parts of fine aluminum powder were stirred in to the mixture followed by 1.04 parts of a solution of hydrogen peroxide. The slurry was then poured into a 2" diameter cartridge and allowed to solidify by cooling. By varying the concentration of the hydrogen peroxide solution from 30% to 5% the density of the final cast was varied from 0.635 to 1.35 g./cc. This cast explosive was capable of being detonated by an electric blasting cap when the density was below 0.8 g./cc., and by a small charge of dynamite when the density was below 1.2 g./cc.

A similar cast with no foaming agent was incapable of sustaining detonation under these conditions. Also a mixture of similar composition prepared from dry solids in a ball-mill was incapable of detonation when boosted with dynamite at a density of 1.0 g./cc. and above.

Example 11 An explosive was made in the same manner as in Example I but with the omission of the aluminum. This explosive, when foamed, had the same sensitivity to initiation both by a cap and by a dynamite booster as that in Example 1. Thus it was much more sensitive than a similar unfoamed explosive, and also more sensitive than a granular explosive of the same composition and density.

Example 111 87.9 parts of ammonium nitrate were heated to about 130 C. with 5.15 parts of water until the whole was liquid. On cooling to 110 C. the mixture was a thick slurry of liquor and crystals and into this mixture were stirred 5.72 parts of parafiin wax (melting point about 55 C.) containing 0.25 part of an emulsifying agent (n-octadecylamine). A wax-in-liquor emulsion was formed, and to this was added 1.0 part of hydrogen peroxide solution of strength between 30% and 5%. After pouring into cartridges the explosive foamed to a density of 0.68 to 1.34 g./cc. and solidified to a rigid cast. In 2" diameter this explosive was sensitive to initiation by an electric blasting cap at a density of 0.95 g./ cc. or less, and by a dynamite booster below a density of 1.2 g./cc. A similar unfoarned explosive would not sustain detonation under these conditions; moreover a similar mixture (without the water) made in a ball-mill from granular ammonium nitrate would not detonate with a dynamite booster at a density of 1.04. Also a sample of this cast explosive which had not been foamed was ground up to pass 14 Tyler mesh and packed into 2" cartridges; under these conditions detonation was not initiated by a cap at densities of 0.89 g./cc. and 0.99 g./cc.

Example IV 83.2 parts of ammonium nitrate were melted at about 130 C. with 5.52 parts of water and allowed to cool to 105 C. 6.41 parts of TNT were stirred into the melt followed by 3.46 parts paraifin wax (melting point about 55 C), both contained about 0.15 part of emulsifying agents. The resulting emulsion was foamed and cast as in earlier examples. However, hydrogen peroxide is not a suitable foaming agent in this case, and sodium nitrite solution (or a metallic carbonate) was used as foaming agent. The resulting explosive was detonated by an electric blasting cap below a density of 1.15 g./cc., whereas an unfoamed mixture made in the same manner was not capable of sustaining detonation in 2" cartridges. In ad dition, a ball-milled mixture of the same composition (less water) was not initiated by a similar cap at densities of 1.05 g./cc.

What I claim is:

1. A cast detonatable explosive composition, having a substantially rigid solid structure withfrom 10% to 50% by volume of gaseous pockets dispersed therein, consisting essentially of an intimate mixture of ammonium ntrate and from 2% to 20% by weight of at least one non-volatile fuel selected from the group consisting of hydrocarbon oils, hydrocarbon waxes, fats, cellulosic materials, urea, graphite, aluminum and ferrosilicon.

2. A cast detonatable explosive as claimed in, claim 1 wherein up to 6.4% by weight of the composition of a highly explosive compound selected from the group consisting of trinitrotoluene, pentaerythritol tetranitrate and cyclotrimethylene trinitramine is incorporated into the explosive composition as part of the fuel.

3. A cast detonatable explosive composition, having a substantially rigid solid structure with from 10% to 50% by volume of gaseous pockets dispersed therein, consisting essentially of an intimate mixture of (i) ammonium nitrate, (ii) from 5.15% to 17.9% by weight of said composition of at least one melting point depressant selected from the group consisting of urea, water and inorganic nitrates, and (iii) from 2% to 20% by weight of said composition of at least one non-volatile fuel selected from the group consisting of hydrocarbon oils, hydrocarbon waxes, fats, cellulosic materials, graphite, aluminum and ferrosilicon.

4. A cast detonatable explosive as claimed in claim 3 wherein up to 6.4% by weight of the composition of a highly explosive compound selected from the group consisting of trinitrotoluene, pentaerythritol tetranitrate and ammonium nitrate and from 5.15% to 17.9% by weight of said composition of at least one melting point depres sant selected from the group consisting of urea, water and inorganic nitrates, (ii) from 2% to 20% by weight of said composition of at least a non-volatile fuel selected from the group consisting of hydrocarbon oils, hydrocarbon waxes, fats, cellulosic materials, graphite, aluminum and ferrosilicon, and (iii) a foaming agent selected from the group consisting of the peroxides of sodium, potassium, barium and hydrogen, metallic nitrites, metallic carbonates and metallic bicarbonates in an amount sufficient to provide a volume of gas of from 10% to 50% by volume of said composition, and causing the resultant mixture to cool and solidify in desired shapes.

6. A process as claimed in claim 5 wherein up to 6.4% by weight of the composition of a highly explosive compound selected from the group consisting of trinitrotoluene, pentaerythritol tetranitrate, and cyclotrimethylene trinitramine is incorporated into the explosive composition as part of the fuel.

References Cited in the file of this patent UNITED STATES PATENTS 

1. A CAST DETONATABLE EXPLOSIVE COMPOSITION, HAVING A SUBSTANTIALLY RIGID SOLID STRUCTURE WITH FROM 10% TO 50% BY VOLUME OF GASEOUS POCKETS DISPERSED THEREIN, CONSISTING ESSENTIALLY OF AN INTIMATE MIXTURE OF AMMONIUM NITRATE AND FROM 2% TO 20% BY WEIGHT OF AT LEAST ONE NON-VOLATILE FUEL SELECTED FROM THE GROUP CONSISTING OF HYDROCARBON OILS, HYDROCARBON WAXES, FATS, CELLULOSIC MATERIALS, UREA, GRAPHITE, ALUMINUM AND FERROSILICON. 